Method of preparing fiber/resin composites

ABSTRACT

Resin compositions useful for filament winding applications comprising an epoxy component including at least one polyepoxide resin curable by heat, an olefinicially unsaturated monomer component including at least one polyolefinically unsaturated monomer curable by actinic radiation, at least one photoinitiator which is not a peroxide, at least one organic peroxide, and a heat activated curing agent for epoxides. The compositions have a viscosity less than about 2000 centipoise (cps) and are capable of retaining this viscosity for at least about 2 hours at a temperature of from about ambient temperature to about 60° C. The resins are capable of being immobilized by actinic radiation exposure and further heat cured without substantial resin drip. One or more organic peroxides are employed, selected from the group of organic peroxides having 10 hour decomposition half lives at temperatures of from about 50° C. to less than about 104° C. Also, fiber resin composites comprising fiber substrates impregnated with the dual-curing resin compositions is disclosed. Also the process for coating fiber substrates with the dual-curing resin compositions is disclosed.

This application is a continuation-in-part of U.S. Ser. No. 08/036,325filed Mar. 24, 1993, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to fiber/resin composites and tomethods of making such composites. In a specific aspect, the presentinvention relates to resin articles comprising arrays of continuousfilaments, such as are formed by filament winding, prepregs and thelike.

2. Description of the Related Art

In the field of composite materials, a variety of fabrication methodsand techniques have come into usage for producing fiber-reinforced resinmatrix materials. Continuous filament processes have evolved which areadapted to automated production of filament-reinforced resin articles.The continuous fiber processes include filament winding, wherein thefilament in the form of discrete strands or roving is coated with aresin, then wound on a mandrel at a predetermined angle and windingthickness to yield composite articles having high strength when theresin borne on the filament is cured.

In order to have commercial utility the polymeric resins employed infilament winding operations must exhibit low initial viscosity and longpot-life in the process systems in which they are employed. Lowviscosity is required in order that deposition of the resin on thefilament be highly uniform in character, as is required to achievesubstantially uniform properties in the final product article. Ifviscosity changes appreciably during the filament winding operation, theapplied resin thickness may change significantly, resulting in localizedstresses or discontinuities in the final product article, productarticles which are not within required dimensional tolerancespecifications, and inadequate curing of the resin. In addition, thetensional forces on the resin impregnated filaments being processed willsignificantly increase as the resin viscosity increases, to such extentthat the filament becomes highly susceptible to snapping, i.e.,tensionally breaking.

Long pot-life of the resin is particularly necessary in filament windingoperations where processing times may be on the order of hours. Sincethe resin is continuously being applied to the filament in theseprocesses, the resin bath or other source of the resin must becontinually replenished with resin coating material, and it is thereforenecessary that the resin not "set up" or gel in the source bath or othersource container and applicating means.

For example, in the fabrication of rocket motors, a resin-bearingfilament is wound onto a solid rocket fuel body. In such applications,since the filament winding operation may take upwards of 6 hours andsince viscosity must be substantially stable during this period, a longpot-life resin is essential, and consequently the filament wound bodymust be rotated until full cure of the resin is achieved, which in thecase of conventional epoxy resins can range from hours (for heat curedresins) to days (for resins cured at ambient temperatures). Continuousrotation of the mandrel and filament winding is essential in such cases,since cessation of rotation would result in the viscous resin saggingand dripping under gravitational forces, resulting in a resin-rich lowerportion of the product article and a resin-poor upper portion of theproduct. Accordingly, it is desirable to cure the fiber array quicklyonce it has been formed.

The difficulties inherent in balancing the properties of long pot-lifeand a quick and easily controlled cure have resulted in the developmentof numerous types of resins. And within each class of resin, attemptshave been made to vary the conditions under which the resins will cureeffectively. The standard resins which have been employed in continuousfilament processes, as well as in other systems of fiber/resin compositemanufacture, generally have deficiencies which have specifically limitedtheir utility in these processes.

The epoxy resins form an extremely important and versatile class ofresins. These resins exhibit excellent resistance to chemicals, willadhere to glass and a variety of other materials, show electricalinsulation properties, and are relatively easy to use. Among the epoxyresins, systems employing epoxy compounds in conjunction witholefinically unsaturated compounds have found wide acceptance in theart. In particular, resins comprising epoxies and acrylates have beenfound to be especially useful. This class of resins includes blends ofepoxies and acrylates ("epoxy/acrylate" resins) as well as compositionswherein the principal resin component is an acrylic acid-modified epoxywherein some or all of the epoxy groups have been consumed to produceunsaturated resins. Partially acrylated epoxies are occasionallyidentified as "dual-functional" compounds since they are designed toexhibit both epoxy and acrylate functional groups on the same molecule.

Within the aforementioned class of epoxy/acrylate systems, compositionshave been generated which are adapted to various cure conditions. Suchcompositions have employed heat curing mechanisms, actinic radiationcuring mechanisms, or a combination of both.

Heat curing alone has several disadvantages including reducing theviscosity of the resin, causing it to become more fluid and therebymaking it more difficult to handle the article, as well as moredifficult to achieve a product of isotropic character. In applicationssuch as filament winding, this drop in viscosity results in resin drip,as previously mentioned. Yet heat curing of epoxy/acrylate systems is aneffective and practical means of curing the resins to the fully hardenedstate that is the source of the resins' great utility.

Heat cured epoxy resin systems are disclosed by U.S. Pat. No. 3,408,422to May et al., U.S. Pat. No. 3,441,543 to Heilman, RE 27,973 (3,594,247)to Pennington et al., U.S. Pat. No. 3,678,131 to Klapprott et al., U.S.Pat. No. 4,017,453 to Heilman et al., U.S. Pat. No. 4,025,578 toSiebert, U.S. Pat. No. 4,447,586 to Shimp, U.S. Pat. No. 4,515,737 toKarino et al., and U.S. Pat. No. 5,011,721 to Decker et al.

Exemplary of heat cured compositions are the compositions of U.S. Pat.No. 3,408,422 to May et al. May et al. discloses compositions of anacrylated epoxy polymer and a hydroxylamine (as a stabilizer), as wellas unsaturated monomers and peroxides having decomposition temperaturesbelow 150° C. The compositions described by May et al. are heat cured,and include curing agents such as "onium" salts.

The use of actinic radiation to cure or partially cure, i.e., gel theresin, can substantially increase the viscosity of the resin on theformed article. Actinic radiation generally cannot induce completehardening of the resin and such systems usually employ a catalyst and/oran additional cure step to fully cure the resins. An example of such aprocess is U.S. Pat. No. 4,892,764 to Drain et al. which employsultraviolet (UV) light induced polymerization, and requires additionalcuring at ambient temperatures for extended periods. The Drain et al.patent also employs an aliphatic diamine catalyst which significantlyreduces the pot-life of the uncured resin. The Drain compositions arenot intended to be heat-cured and as a result exhibit low glasstransition temperatures (T_(g)), thereby having limited utility inapplications where the temperature resistance of the cured resins iscritical.

Other UV curing systems are found in U.S. Pat. No. 3,922,426 to Feltzindescribing filament wound articles impregnated with an ultraviolet lightcurable resin comprising an unsaturated polyester, an unsaturatedmonomer, an organic peroxide, and a photosensitizer. More specifically,Feltzin discloses organic peroxides with half-lives at temperaturesbetween 26° C. and 172° C. which are required to be used in combinationwith a photosensitizer. This wide range of half-life temperature isuseful in Feltzin because of the incorporation of the photosensitizer.Other filament winding systems using UV or other actinic radiation tocure resins include U.S. Patent Nos. 3,660,144, 3,660,145 and 3,660,371to Johnson et al., U.S. Pat. No. 3,772,062 to Shur et al., and U.S. Pat.No. 4,479,984 to Levy et al.

Traditionally, dual-curing epoxy/acrylate systems, i.e., systems whichemploy both an initial actinic radiation exposure and a subsequentthermal polymerization step, have been used for numerous purposesincluding adhesives, coatings, and prepregs such as those involvingfilament winding. Such dual-curing prepreg compositions have employedblends of epoxies and acrylates, epoxy curing agents andphotoinitiators.

Dual-curing compositions of this kind are described in U.S. Pat. No.4,092,443 to Green. Green discloses dual-cured filament impregnatingresin compositions including a heat curable epoxide orepoxide-containing compound, a photopolymerizable component, such asacrylates, methacrylates and other polyolefinically unsaturatedcompounds. Heat activated curing agents such as amines, borontrihalides, imidazoles, and anhydrides, as well as optional use ofphotocatalysts, such as phenones and photo-activated organic peroxides,are also disclosed. The Green compositions, however suffer from a numberof the disadvantages associated with dual-cured systems. Principally,these compositions provide little or no resistance to resin drip duringthe heating step. Articles formed from the Green compositions andprocess therefore require rotation during heating in order to retainuniformity of resin distribution and the isotropic characteristics andproperties dependent thereon.

U.S. Pat. No. 3,937,855 to Gruenwald describes the impregnation ofinsulated electromagnetic coils with dual-curing resin compositions. Thepreferred compositions are polyesters solubilized in unsaturatedmonomers and mixed with peroxides activated by high temperatures alongwith accelerators such as a tertiary amine or an organo-cobalt compound.The resins described by the Gruenwald patent are quickly gelled byexposing the surface of the applied resin to a highly reactive chemicalcross-linking agent, i.e., organic peroxides such as methyl ethyl ketoneperoxide, cyclohexanone peroxide, diacetyl peroxide, dilauryl peroxide,cumyl hydroperoxide and benzoyl peroxide. Alternatively, the quickgelation of the resin at the periphery at ambient temperature can beaccomplished by incorporation of a photo activator such as a benzoinether and exposure of the resin to UV light.

U.S. Pat. No. 4,230,766 to Gaussens et al. discloses dual-curingcompositions of (meth)acrylated epoxy resins, unsaturated monomers,photoinitiators, and organic peroxides. The resins of the Gaussens etal. patent are cured first by ultraviolet light exposure and heatexposure as a second cure step. The peroxides disclosed by Gaussens etal. include lauroyl peroxide and benzoyl peroxide.

U.S. Pat. No. 3,935,330 to Smith et al. describes dual-curing resinsincluding polyepoxide monomers or polymers, urea/formaldehyde resins, ora melamine/formaldehyde resin, and a thermally curable cross-linker. Thecompositions described by Smith et al. may also include adual-functional (meth)acrylamide having at least one double bond and atleast one oxirane group. Another component of the compositions includesan ultraviolet light sensitive acrylate. Free radical initiators areincluded such as organic peroxides including di-t-butyl peroxide,benzoyl peroxide, t-butyl hydroperoxide, perbenzoic acid, and t-butylperacetic acid. Smith et al. also disclose photosensitizers includingphenones. The compositions disclosed by Smith et al. are described asbeing cured by an ultraviolet light exposure and are subsequentlyexposed to heat.

None of the aforementioned patents disclose dual-curing filament windingor prepreg resin compositions resistant to the resin sag and drip causedby heat curing. Other measures have generally been needed includingspraying a curing agent onto an uncured wound article, e.g., U.S. Pat.No. 3,937,855 to Gruenwald or, more commonly, requiring that the woundarticle be rotated during the heat cure.

Therefore, it would be a significant advance in the art to overcome theabove-described difficulties associated with filament winding processes,in a manner which would obviate the use of additional curing steps andlong rotation periods heretofore necessary to obtain quality compositeshaving uniform characteristics.

The present invention solves the disadvantages inherent in the prior artby providing compositions that maintain stable low pot-life viscositiesfor a significant period of time such that commercial filament windingprocesses are practicable. The compositions of the present inventionalso exhibit relatively high glass transition temperatures and areintended to be useful in high temperature applications. Unexpectedly,the resin compositions of the present invention allow uniform propertiesof the cured product to be obtained without drip or excessive flow ofthe resin during the heat-cure stage.

Accordingly, it is an object of the present invention to provide animproved process for forming fiber/resin composites.

It is a further object of the invention to provide an improved processfor filament winding which overcomes the above-described deficiencies ofthe prior art practice of these processes.

It is another object of the invention to provide filament wound articleswhich are readily and economically formed, and which are rapidlyprocessed for subsequent handling, packaging, or other processingoperations.

Other objects and advantages of the present invention will be more fullyapparent from the ensuing disclosure and appended claims.

SUMMARY OF THE INVENTION

In one aspect, the present invention relates to resin compositionsuseful for filament winding applications. The compositions include anepoxy component including at least one polyepoxide resin curable byheat, an olefinically unsaturated monomer component including at leastone polyolefinically unsaturated monomer curable by actinic radiation,at least one photoinitiator which is not a peroxide, at least oneorganic peroxide having the specified ten hour half-life decompositiontemperature, and a heat activated curing agent for epoxides. Thecompositions of the present invention have an initial viscosity lessthan about 2000 centipoise (cps), and are capable of retainingsubstantially the same viscosity for at least about 2 hours, andpreferably about 4 to 8 hours, at temperatures ranging from aboutambient temperature up to about 60° C. On being exposed to actinicradiation the compositions are capable of being immobilized to a gelledstate which will resist substantial resin drip during the heat cureprocess.

The resin compositions include an organic peroxide selected from thegroup of organic peroxides having 10 hour decomposition half lives attemperatures of from about 50° C. to less than about 104° C. Peroxidesoutside of the upper range have generally not been found to be effectiveat preventing resin drip. In general, useful peroxides include diacylperoxides, peroxydicarbonates, peroxyesters, and peroxyketals. Mixturesof peroxides are also contemplated.

Polyepoxide resins useful in the resins of the present invention may beselected from the classes consisting of polyglycidyl andpoly(β-methylglycidyl)ethers of dihydric and polyhydric alcohols andphenols, novolaks, alkyl-substituted phenols and halogen-substitutedphenols; poly(N-glycidyl) compounds obtained from amines containing atleast 2 amino-hydrogen atoms; triglycidylisocyanurate; N,N'-diglycidylderivatives of cyclic alkaline ureas and hydantoins; andpoly(S-glycidyl) derivatives of dithiols. Mixtures of these resins arealso useful.

The compositions of the present invention contain at least onepolyolefinically unsaturated monomer selected from the group consistingof acrylic and methacrylic resins, vinyl monomers, and unsaturatedpolyesters solubilized in vinyl monomers. The compositions may alsoinclude one or more mono-olefinically unsaturated monomers useful asdiluents.

Useful photoinitiators include substituted benzophenones and substitutedacetophenones, benzoin and its alkyl ethers, xanthone and substitutedxanthones. Mixtures of these compounds may be employed.

The resins contain at least one heat activated curing agent. The curingagent may be an amine-containing compound or an anhydride. Whenamine-containing curing agents are employed they may be selected fromthe group consisting of dicyandiamides, boron trifluoride:aminecomplexes, boron trichloride:amine complexes, latent amine curatives,tertiary amines, aromatic polyamines, and imidazoles. Mixtures of curingagents are also contemplated. Alternatively, the resins may contain apolycarboxylic acid anhydride heat activated curing agent. The anhydridecuring agents are generally employed in combination with a minor amountof an amine-containing accelerator for increased cure speed. When theanhydride curing agent is used, the accelerator may also be selectedfrom the group consisting of dicyandiamides, boron trifluoride:aminecomplexes, boron trichloride:amine complexes, latent amine curatives,dissociable amine salts such as the tri(2-ethyl-hexanate) salt oftris(dimethylamino-methyl)-phenol and the like, tertiary amines,aromatic polyamines, and imidazoles.

In another embodiment, the present invention includes a process forproducing fiber/resin composites comprising a fiber substrate and adual-cured resin composition. The resin composition will comprise atleast one polyepoxide resin curable by heat, at least onepolyolefinically unsaturated monomer which when subjected to sufficientactinic radiation immobilizes the polyepoxide resin, a photoinitiator,an organic peroxide having a 10 hour decomposition half life at atemperature of from about 50° C. to less than about 104° C., and atleast one heat activated curing agent for epoxides. In this process thefiber resin composite is initially cured by exposure to actinicradiation sufficient to immobilize the polyepoxide resin so that theresin exhibits no resin drip when subjected to a further heat cure step.

In another aspect, the present invention includes fiber/resin compositesformed by the process of applying a liquid resin, having a viscosity ofabout 2000 centipoise (cps) or less and a pot-life of at least 2 hours,and preferably 4 to 8 hours, at temperatures ranging from about ambienttemperature to about 60° C., to a fiber, subjecting the fiber/resincomposite to actinic radiation sufficient to permanently immobilize theresin, and then subjecting the fiber resin composite to heat sufficientto cure the resin. The resin composition comprises a heat curablepolyepoxide resin, an actinic radiation curable polyolefinicallyunsaturated monomer, a photoinitiator, an organic peroxide having a 10hour decomposition half life at a temperature of from about 50° C. toless than about 104° C. and a heat activated curing agent for epoxides.

DETAILED DESCRIPTION

Product articles according to the present invention may be made by anyof a wide variety of fiber/resin composite forming methods, includingthose utilized in forming fiber/resin matrices comprising discontinuousfibers. For example, lay-up techniques, sheet molding, resin transfermoldings, etc., as well as methods applicable to the use of continuousfilament, such as filament winding, braiding, and pultrusion may beused. Further, fiber/resin composite articles may be formed by acombination of these methods, such as where a solid rod is formed bypultrusion and subsequently used as the core body for filament winding.

In one preferred embodiment, the articles produced according to theinvention may comprise a filament array of substantially parallellyaligned, laterally continuous filaments which have been impregnated withthe resin compositions of the invention and subjected to actinicradiation curingly effective for the actinic radiation curable resincomponent of the composition.

As used herein, the term "laterally continuous", when used to describefilament arrays of parallelly aligned filaments, means that the adjacentfilaments in the parallelly aligned array have the resin compositionbetween their facing surfaces, without gross voids, spaces, ordiscontinuities therebetween. The resin composition possesses sufficientflow characteristics, as distinct from drip or sag, to uniformly bindadjacent filaments together.

In producing filament wound articles according to the present invention,wherein the filaments are treated, i.e., coated or impregnated, with theresin composition, the actinic radiation may be applied to the filamentprior to, simultaneously with, or subsequent to winding of the treatedfilament onto the substrate mandrel. Such concurrent actinic irradiationof the resin borne on the filament facilitates a high degree ofprocessing flexibility in the fabrication of such filament woundarticles. In this manner, winding of articles of substantially irregularshape is facilitated because irradiating impregnated fibers prior tosubstrate contact can impart sufficient adhesive and tack qualities tocause the fiber to adhere to the substrate and/or each other whilepassing over areas where slippage would normally occur. Thus, in someinstances, it may be advantageous to irradiate the impregnated filamentprior to its application by winding onto the substrate. Alternatively itmay be desirable to filament wind the mandrel, and subsequently toirradiate the wound article.

Similarly, in the pultrusion formation of filament articles according tothe present invention, an array of parallelly aligned filaments ispultruded through a die imparting a selected cross-sectional shapethereto, the filament having been impregnated with the resin compositionof the invention. The resulting shaped filament array is subjected tocuringly effective actinic radiation concurrently with its passagethrough the die. Such concurrent irradiation may be effected eitherprior to or subsequent to passage of the filament array through the die,insofar as the ultimate shape is imparted somewhat upstream of the diein proximity to the forming die openings. In a specific application, theparticular placement and operation of the actinic radiation source foreffectuating curing will be readily determinable by those skilled in theart without undue experimentation.

The use of UV light provides significant processing and handlingadvantages during manufacture by instantly immobilizing the resin.Immobilization of the resin is controlled to provide sufficient gelationto prevent flow out of the part but allow good wetting between layers,thus assuring even resin distribution, reduced void formation and easeof handling of the finished part without resin migration, sagging ordripping. The rapid gelation stage, in most cases, also eases handlingduring the heat-cure.

Advantages of the present invention include elimination of runs, drips,migration, and resin-rich/resin-poor areas; curing of the resin whileparts are stationary, i.e., no requirement for rotation; a process whichyields even resin distribution, reduced voids, lessens clean up andreduces resin usage and waste; and the low initial viscosity promotesexceptionally fast filling of parts and composite structures which canbe rapidly controlled by UV radiation.

The filament winding processes used with the present compositions arefor the most part continuous processes. Typically, the resin compositionis housed in an open vessel beneath a rotating roller. The rotatingroller is partially submerged in the resin so as to coat the roller asit rotates. Fiber is drawn from a spool and directed through the resinand into contact with the roller surface, whereby the fiber is coatedwith resin as it passes. Actinic radiation is directed at the coatedfiber as it leaves the roller, thereby gelling and immobilizing theresin. The gelled resin is wound on a mandrel, as previously described,and may be further cured, if desired or necessary, by actinic radiationprior to heat cure.

Subsequent to winding, the formed article is placed in an oven at anappropriate cure temperature. In general, the compositions or thepresent invention can substantially reach a fully cured state by heatcuring at about 150° C. to about 200° C. for about two to four hours. Itwill be appreciated by those skilled in the art that the time andtemperature of the heat cure may be varied to reach particular desiredresults.

As described hereinabove, the Drain compositions are designed to becured at room temperature. Thus, there is inherently a certain amount ofresistance to drip and sag of the resin under the forces of gravity,since UV radiation and ambient temperatures are sufficient to ensurecure. Ambient temperature curing epoxy resins as used in Drain can beaccelerated if exposed to mild temperatures, but less than high heatcuring (>100° C.) temperatures. These ambient curing epoxy resins cureso quickly when exposed to heat that there is little chance for them toliquify and drip or sag. Furthermore, there is little need to acceleratethe cure by using heat since it does not contribute to increased T_(g)and is costly. The Drain compositions suggest solving the resin drip orsag problem using UV cure combined with ambient epoxy cure systems whichdo not exhibit this problem. It is also interesting to note that Drainteaches the equivalency of azo compounds, benzoyl peroxide and cumenehydroperoxide as being useful infrared initiators. Because the Draincompositions are not truly intended to be heat-cured, there is thereforeno need to be concerned with the addition of a catalyst component whichprevents resin drip during a heat cure stage. Additionally, the presentinvention is directed away from the use of azo compounds due to theirliberation of nitrogen gas, which causes bubbles in the composite. Thepresent invention also cannot employ cumene hydroperoxide because itsten hour half life decomposition temperature (150° C.) is well outsidethe operable range of the present invention. The ten hour half life isirrelevant to Drain since his use of the aforementioned infraredinitiators are not involved in a heat cure stage. Furthermore, in orderto effectuate photo decomposition of benzoyl peroxide, it is generallyaccepted that a photosensitizer must be present. This is discussed in"The Photosensitized Decomposition of Peroxide", Walling et al., JrnlAmer. Chem. Soc., 87:15, Aug. 5, 1965. This article bases its analysison the assumption that little decomposition of benzoyl peroxide can beinduced by photolysis. Additionally, benzoyl peroxide is discussed inthe journal Polymer, 1973, volume 14, October, page 527 In an articlewritten by SenGupta et al. This article reports on a study ofphoto-dissociation of benzoyl peroxide and concludes that there is noevidence for significant production of benzoyl radicals duringphotolysis of benzoyl peroxide at wave lengths exceeding about 3,000 Å(300 nanometers). It should be mentioned that the UV range isapproximately 200-400 nanometers. It would appear, therefore, thatalthough benzoyl peroxide is mentioned as an infrared initiator, whichis reportedly distinct from a UV photoinitiator in accordance withDrain, its ability to perform this function under actinic is notgenerally accepted as being effective.

The functions of photoinitiators and photosensitizers are often confusedin the art. These compounds are distinct in their chemical makeup aswell as their mechanisms and roles. Compounds which are consideredphotoinitiators generally directly absorb a particular range of lightwavelengths, become excited and decompose to generate a free radical.This free radical then initiates polymerization and subsequent cure ofthe monomer in which the photoinitiator is immersed. Photosensitizers,on the other hand, absorb light energy but do not directly produce afree radical. Instead, their absorbed light energy is transferred toanother compound which is capable of generating a free radical undercertain conditions. One example of this is given in U.S. Pat. No.3,922,426 to Feltzin. This reference describes the process of preparinga filament wound article using a photopolymerizable resin matrix and acuring system which uses a photosensitizer in combination with anorganic peroxide. This combination is discussed as being critical, sincethe photosensitizer must absorb the light energy and transfer it to theorganic peroxide in order to begin a free radical reaction. This islargely due to the fact that organic peroxides per se do not inthemselves have a high capacity for absorbing light. The ability toabsorb light is generally measured as a function of the extinctioncoefficient at a particular wavelength. The higher the extinctioncoefficient, the greater the absorption of the energy at that wavelengthand the faster and more complete generation of a free radical, willoccur. Thus, while benzoyl peroxide in combination with a sensitizer,will according to Feltzin be effective in photocuring a resincomposition, benzoyl peroxide on its own is not an effectivephotoinitiator. This must be taken into account when the reference inDrain to benzoyl peroxide being an infrared initiator is made. If thebenzoyl peroxide operates in Drain as an infrared initiator, its speedis extremely slow, since its ability to absorb light and thereforegenerate a free radical is not particularly good. As previouslydiscussed in Drain, there is no intention to use high temperature cureand therefore no concern about resin drip due to fluid movement duringsuch heat exposure.

The present invention also seeks to use epoxide resins which are capableof high temperature cure and therefore yield a high T_(g). This is alsodistinct from references such as Drain which, as previously described,use ambient temperature epoxy curing agents which would not be operablein the present compositions.

U.S. Pat. No. 4,092,443 to Green discusses two main classes ofphotocatalysts. The first class is a photoinitiator class. As previouslydiscussed, radicals are directly formed from the photoinitiator compoundand this radical then initiates polymerization of a monomer. The secondclass described by Green are photosensitizers. His definition issubstantially the same as given hereinabove. However, in a furtherdiscussion of the first class (photoinitiators) of photopolymerizablecompounds, Green confuses photoinitiators with photosensitizers. Forexample, he includes organic peroxides and acetophenones as both beingphotoinitiators. The suggestion that acetophenones, which arephotosensitizers or, in other words, promoters for photoinitiators, areequivalent to known photoinitiators is technically incorrect. Theacetophenones, benzophenones, alkyl ethers and O-alkoxycarbonylderivatives of an oxime or benzil are all photosensitizers which promotethe formation of a radical on the peroxide. As previously mentioned,peroxides are generally not considered photoinitiators in themselves,and generate few radicals when exposed to light unless they are coupledwith a photosensitizer. This view is further supported by theaforementioned Feltzin patent, Table II, where a number of acetophenonesare shown as photosensitizers for the organic peroxide he discloses.

It is clear that in combination with a photosensitizer, virtually anyperoxide can be used to generate a free radical using actinic radiation.In the absence of a photosensitizer, organic peroxides are generally notuseful as photoinitiators in themselves.

The present invention has discovered that the resin drip and sag whichoccurs due to the flow of uncured material under high temperature curingconditions, can be prevented through the incorporation of an organicperoxide falling within the specified and critical ten hour half-lifedecomposition temperature range. The present invention incorporatesthese specified organic peroxides for their ability to generate the freeradicals during the heat cure and polymerize any uncured olefinicallyunsaturated monomer, the final curing of which is necessary to preventthe flow of the epoxy resin which results in resin sag. Thus, byincorporating a three component cure system, namely a photoinitiatorwhich is not a peroxide, a heat activated organic peroxide having aspecific ten hour decomposition half-life temperature range and which isunreactive in the presence of actinic radiation and in the absence of aphotosensitizer, and a heat activated curing agent for an epoxycomponent, the aforementioned problems with resin drip and sag areovercome, and pot life stability as well as enhanced uniformity andquality of composite parts formed therefrom is achieved.

It should be mentioned that the production of free radicals usingactinic radiation must be sufficiently high to work effectively infilament winding compositions. If the photoinitiator does not have asufficient rate of decomposition, than the olefinically unsaturatedmonomer will not be sufficiently immobilized and sufficiently partiallycured to hold the epoxy component on the fiber. Additionally, without aheat activated organic peroxide to finish the cure of the olefinicallyunsaturated monomer, resin sag would occur. Thus, the choice ofphotoinitiators for the present invention cannot from any practicalpoint of view include peroxides.

It is also unexpected that the combination of an organic peroxide and anamine or amine-containing compound would produce a stable formulation.This is because even small amounts of amines are known to react withperoxides. Additionally, metal ions enhance the rate of reaction ofamines with peroxides. This is discussed in Chemistry Of Peroxides,Patai, Saul Editor, pages 251, 286 and 352, John Wiley & Sons, 1983.This references discloses that amines can decompose peroxides and wouldteach away from mixing an amine and peroxide if a long pot-life isdesired. The reaction of an amine with a peroxide would be expected toproduce unwanted reaction products and in the process would consume theperoxide and amine curing agents which are necessary components of thethree component cure system of the present invention. It has beensurprisingly and unexpectedly discovered, however, that this reactiondoes not have any effect on the present invention and that the excellentpot-life necessary for filament winding applications is achieved.

The dual curing filament winding resins of the present invention areformulated with the aforementioned polyolefinically unsaturatedmonomers, and preferably polyacrylate monomers, that form a cross-linkedgel upon exposure to actinic radiation, and preferably UV light. Thiscross-linking prevents resin dripping from the part during the winding.The organic peroxide component of the present invention serves to cureany unpolymerized olefinically unsaturated monomer during the heat curestage. The organic peroxide ensures that the olefinically unsaturatedmonomer provides a sturdy matrix to prevent unwanted drip of epoxy.However, when certain fibers are employed that screen UV light, such asgraphite or Kevlar, or when using high winding speeds with most fibers,a portion of the acrylate can remain uncured after exposure to UV light.Thus, although the resin does not drip off the part during filamentwinding, it may tend to drip during the heat-cure cycle unlessappropriate measures are taken to reduce the flowability of the resin.

The degree of gelation (initial immobilization) of a given resincomposition will largely depend on the amount and type of actinicradiation to which it is exposed. Exposure time is easily controllable,as is the intensity and type of radiation. These parameters are easilydeterminable by ode reasonably skilled in the art, and may vary inaccordance with the choice of resin composition, fiber substrate andtype of product desired. A single actinic source, for example UV light,or alternatively multiple sources of light, may be focused on the resincoated fiber to effectuate gelation. The winding speed can also beclosely controlled, thereby controlling the duration of exposure of theresin coated fiber to the beam of radiation. In certain commercialapplications, winding speeds of about 12 inches/second to about 20inches/second are useful. Radiation intensities of, for example UVlight, may be from about 120 milliwatts/cm² to about 180 milliwatts/cm².These ranges are not in any way intended to be limiting of the presentinvention, but are merely illustrative of certain useful ranges. Otherwinding speeds and intensities of light may easily be chosen by thoseskilled in the art.

In addition, the dilution of the polyolefinically unsaturated portion ofthe composition by the unreacted epoxy system, and the increasedviscosity that occurs upon gelation, together can reduce the degree ofvinyl reaction relative to a 100 wt. % vinyl composition, furtherimpeding the thoroughness of the cross-linking and reducing the resin'scapacity to resist dripping when heated.

The inclusion of a thermally activated radical source, i.e., a peroxide,will increase the extent of the vinyl reaction as the composition isheated. One effect of a more complete vinyl reaction is to compensatefor the decreased viscosity that occurs as the composition heats up tothe heat cure onset temperature of the major components (usually aheat-curing epoxy system). Another effect is to compensate for possibleinadequacies in the geometry of the actinic cure step where exposure ofthe resin is not optimal. The peroxide enables the further extension ofthe gelation and cure of the resin to any portions of the resin whichare less fully exposed to the actinic source. The intent is to retain atacky, relatively soft gel during the application stage, so as toimprove adhesion and facilitate handling during fabrication, while atthe same time producing a composition which will not drip during thecuring heat-up stage.

While not wishing to be bound by any one theory, applicants believe thatthe peroxide plays a role in the reaction of unreacted vinyl groupstrapped in the epoxy resin diluted gel formed during the irradiationstage. Normally, it would be expected that these groups might thermallypolymerize during the final high temperature epoxy cure. It is possible,however, that the more extensive vinyl polymerization at a lowertemperature, produced by initiation using a suitable peroxide, leads toa stronger structure when the anhydride-hydroxyl reaction takes over inthe case of the anhydride curing compositions. Alternatively, theperoxide may be producing direct vinyl bonding to the cured epoxy byabstraction on epoxy compounds followed by vinyl addition to the newradical sites.

As was discussed above, the resin component of the prior art partiallycured filament wound articles will tend to drip upon heating, generallyrequiring the rotation of the articles during heat curing to avoidanisotropies. For example, amine curing resin formulations, inaccordance with the present invention but containing no peroxide, wereused to form composite articles as described elsewhere herein. Articleswere formed by filament winding onto mandrels to which thermocouples hadbeen attached, and the rise in temperature of the article during heatcure was then correlated with the onset of resin drip.

It was observed that the onset of the drip of the amine curing resins ofthe present invention will occur, in the absence of peroxide, generallyin the range of from about 80° C. to about 100° C., depending upon thecomposition of the resin. The peroxide chosen for use in any particularresin formulation will therefore depend in part on the resin drip onsettemperature of the formulation. To be useful for the present invention,the peroxide selected must provide sufficient additional cross-linkingof the gel to offset any decrease in resin viscosity that wouldotherwise occur during the heat-up process. In addition, for the benefitof the peroxide to be obtained, the offsetting cross-linking induced bythe thermally activated peroxide must occur at a temperature below ornear the temperature at which the drip phenomenon begins. Because thedecomposition of each peroxide is expressed as a ten hour half-lifefunction of temperature, a peroxide will begin to decompose attemperatures below its ten hour half-life temperature (T_(1/2)). Theperoxide can therefore begin to cross-link the gelled resin before thetemperature rises sufficiently to otherwise cause the resin to drip. Theperoxides useful in the present invention must have a T_(1/2) less thanabout 104° C. Peroxides having T_(1/2) 's of about 104° C. or greaterhave not been found to be useful in the resins of the invention. It isbelieved that such peroxides do not generate sufficient cross-linking ofthe gel until after resin drip has begun during the heat-up process.

Thus, a range of epoxy/polyolefinically unsaturated monomer formulationshas been developed. These compositions are designed to form a soft gelwhich allows for interlayer wetting when exposed to UV radiation. Thecompositions are further designed to retain their non-flow propertiesduring the heat-up stage of heat-curing by producing additionalimmobilizing cross-linking during the heat-up. This is accomplished bymeans of a thermally activated radical source in the formulation, namelythe class of peroxides described herein.

A peroxide, which decomposes on heating to form radicals is added to theformulation to initiate the polymerization of any unreactedpolyolefinically unsaturated monomer. The choice of peroxide is criticalto prevent dripping during heat-cure. The peroxide must possess a 10hour half-life decomposition temperature of less than 104° C. A peroxidewith a higher value decomposes too slowly and the polyolefin does notpolymerize sufficiently to prevent dripping during the heat-cure.

A preferred class of compositions of the present invention are the"amine curing resins". These amine curing resins are created by mixingan epoxy resin component comprising at least one polyepoxide, apolyolefinic component including at least one polyacrylate, aphotoinitiator which is not a peroxide, and a peroxide falling withinthe inventive specified ten hour half-life temperature range, with acuring component comprising an amine-containing heat activated curingagent. Separately, the two components (epoxy component and curingcomponent) of the amine curing resins have essentially unlimited shelflife. When mixed, the compositions can retain a usable viscosity(pot-life) i.e., less than about 2000 centipoise (cps), for a minimum ofabout 2 and preferably about 4 to 8 hours at temperatures ranging fromabout ambient temperature to about 60° C. The amine curing resincompositions have a T_(g) in the range of about 110° C. to about 160° C.when fully cured.

The amine curing resins of the present invention have an epoxy componentpresent in an amount ranging from about 60 wt. % to about 85 wt. %, andpreferably, about 63 wt. % to about 75 wt. %; a polyolefinic componentpresent in an amount ranging from about 5 wt. % to about 30 wt. %, andpreferably from about 10 wt. % to about 20 wt. % of the composition.Most preferably the polyolefin component is present at about 15 wt. % ofthe composition. The amine-containing heat activated curing agent isgenerally present in an amount ranging from about 2 wt. % to about 10wt. %, and preferably from about 3 wt. % to about 6 wt. %. Mostpreferably the heat activated curing agent is present in an amount ofabout 5.5 wt. %. The photoinitiator is generally present in an amountranging from about 1 wt. % to about 10 wt. %, and most preferably fromabout 2 wt. % to about 5 wt. %. The heat-generated free radicalinitiator (organic peroxide) is present in an amount ranging from about0.2 wt. % to about 2 wt. %, preferably from about 0.5 wt. % to about 1.5wt. %. Miscellaneous additives such as wetting and defoaming agents canbe added collectively in amounts of about 0.5 to about 1% by weight ofthe composition, added as part of the resin component. Optionally, fireretardant materials such as phosphorous-containing compounds may bepresent in amounts of about 2% to about 10%, and preferably about 3% toabout 5% by weight of the composition.

Another preferred class of compositions of the present invention are the"anhydride curing resins". These compositions comprise a mixture of anepoxy resin component including at least one polyepoxide, a polyolefiniccomponent including at least one polyacrylate, a photoinitiator which isnot a peroxide, and a peroxide falling within the specified ten hourhalf-life decomposition temperature, with a curing component comprisinga carboxylic acid anhydride and an anhydride accelerator. The anhydridecuring compositions exhibit a T_(g) of from about 110° C. to about 160°C. when fully cured. The anhydride curing compositions also generallyexhibit lower viscosities than the amine curing resins of the presentinvention. Because the reaction between the epoxy and the anhydride isinherently slower than with amine curing agent, the anhydride curingresins have a greater pot-life capability, e.g., at least a 24 hourpot-life.

In the anhydride curing compositions of the present invention, the epoxycomponent may be present in amounts ranging from about 37 wt. % to about48 wt. % of the composition, most preferably from about 40 wt. % toabout 45 wt. % of the composition. The anhydride component may bepresent in amounts ranging from about 33 wt. % to about 43 wt. %, mostpreferably from about 36 wt. % to about 41 wt. % of the composition. Theanhydride accelerator may be present in an amount of about 0.1 wt. % toabout 5.0 wt. %; preferably in an amount of about 1.0 wt. % to about 2.0wt. %. The polyolefinic component may be present in an amount rangingfrom about 10 wt. % to about 30 wt. %, preferably from about 10 wt. % toabout 20 wt. % and most preferably about 12 wt. % to about 15 wt. %. Thephotoinitiator is present in an amount ranging from about 1 wt. % toabout 10 wt. %, and preferably from about 1.5 wt. % to about 5 wt. %.The heat-generated free radical initiator (organic peroxide) may bepresent in amounts ranging from about 0.2 wt. % to about 2 wt. %, andpreferably from about 0.3 wt. % to about 1 wt. %. Miscellaneousadditives such as wetting and defoaming agents can be added collectivelyin amounts of about 0.5 to about 1% by weight of the composition, addedas part of the resin component. Optionally, fire retardant materialssuch as phosphorous-containing compounds may be present in amounts ofabout 2% to about 10%, and preferably about 3% to about 5% by weight ofthe composition.

Epoxy resins useful in the compositions of the present invention includepolyepoxides curable by elevated temperature. Examples of thesepolyepoxides include polyglycidyl and poly(β-methylglycidyl) ethersobtainable by reaction of a compound containing at least two freealcoholic hydroxyl and/or phenolic hydroxyl groups per molecule with theappropriate epichlorohydrin under alkaline conditions or, alternatively,in the presence of an acidic catalyst and subsequent treatment withalkali. These ethers may be made from acyclic alcohols such as ethyleneglycol, diethylene glycol, and higher poly(oxyethylene) glycols,propane-1,2-diol and poly(oxypropylene) glycols, propane-1,3-diol,butane-1,4-diol, poly(oxytetramethylene) glycols, pentane-1,5-diol,hexane-2,4,6-triol, glycerol, 1,1,1-trimethylolpropane, pentaerythritol,sorbitol, and poly(epichlorohydrin); from cycloaliphatic alcohols suchas resorcinol, quinitol, bis(4-hydroxycyclohexyl)methane,2,2-bis(4-hydroxycyclohexyl)propane, and1,1-bis(hydroxymethyl)cyclohex-3-ene; and from alcohols having aromaticnuclei, such as N,N-bis(2-hydroxyethyl)aniline andp,p'-bis(2-hydroxyethylamino)diphenylmethane. Or they may be made frommononuclear phenols, such as resorcinol and hydroquinone, and frompolynuclear phenols, such as bis(4-hydroxyphenyl)methane,4,4'-dihydroxydiphenyl, bis(4-hydroxyphenyl) sulphone,1,1,2,2-tetrabis(4-hydroxyphenyl)ethane,2,2,-bis(4-hydroxyphenyl)propane (otherwise known as bisphenol A),2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane, and novolaks formed fromaldehydes such as formaldehyde, acetaldehyde, chloral, andfurfuraldehyde, with phenols such as phenol itself, and phenolssubstituted in the ring by chlorine atoms or by alkyl groups eachcontaining up to nine carbon atoms, such as 4-chlorophenol,2-methylphenol, and 4-t-butylphenol.

Poly(N-glycidyl) compounds include, for example, those obtained bydehydrochlorination of the reaction products of epichlorohydrin withamines containing at least two amino-hydrogen atoms, such as aniline,n-butylamine, bis(4-aminophenyl)methane, andbis(4-methylaminophenyl)methane; triglycidyl isocyanurate; andN,N'-diglycidyl derivatives of cyclic alkylene ureas, such asethyleneurea and 1,3-propyleneureas, and of hydantoins such as5,5-dimethylhydantoin.

Epoxide resins having the 1,2-epoxide groups attached to different kindsof hereto atoms may be employed, e.g., the N,N,O-triglycidyl derivativeof 4-aminophenol, the glycidyl ether-glycidyl ester of salicylic acid,N-glycidyl-N'-(2-glycidyloxy-propyl)-5,5-dimethylhydantoin, and2-glycydyloxy-1,3-bis(5,5-dimethyl-1-glycidylhydantoin-3-yl)propane.

Such epoxies are available from a variety of commercial sources, such asthe EPON series from Shell Chemical Co., the EPI-REZ series fromRhone-Poulenc, the Araldite series from Ciba-Geigy, the D.E.R. seriesfrom Dow Chemical Co., and the EPOTUF series from Reichhold.

Also useful are halogenated epoxy resins such as the brominated epoxidesavailable from the sources shown above. Halogenated epoxy resins incombination with other fire retardant materials may be suitable for useas fire retardant additives in the compositions of the presentinvention.

Especially preferred epoxy resins useful in the present invention arethe diglycidyl ethers of hisphenol A marketed under the tradenames EPON825 and EPON 828 available from Shell Chemical Co., D.E.R. 331 and 332available from Dow Chemical Co., and the cycloaliphatic epoxy resinmarketed as ERL-4221 by Union Carbide Co.

Epoxy resins which do not appreciably crystallize at room temperatureover time are preferred. In one embodiment, a blend of epoxy resinscomprising non-crystallizing (Bisphenol F) and those which tend tocrystallize (Bisphenol A) is found to be advantageous.

Various epoxies such as the glycidyl ethers marketed as the EPODILseries by Pacific Anchor Chemical Corporation, a division of AirProducts and Chemicals Inc., may be added as epoxy diluents, to reducethe viscosities of the resins of the present invention.

It will be understood that the foregoing list of epoxy compounds isintended only to be illustrative in character, and that other compoundshaving 1,2 epoxide functionality and curable by heat may potentially beemployed. Other optional epoxy compounds may be present which have bothepoxy functionality and olefinically unsaturated functionality("dual-functional" resins).

Suitable polyolefinically unsaturated components of the compositions mayinclude poly(meth) acrylic resins, polyvinyl monomers, andpolyunsaturated polyesters solubilized in vinyl monomers. As usedherein, the term "(meth)acrylic" is intended to be broadly construed toinclude acrylic as well as methacrylic compounds, e.g., acrylic estersand methacrylic esters.

It is preferred that the polyolefinically unsaturated monomer have a lowviscosity to offset the effect of any higher viscosity component so asto retain the low composition viscosity required for effective filamentwinding. In addition, the polyolefinically unsaturated monomer componentmay comprise one or more low viscosity monoolefinically unsaturatedmonomers as diluents, but in any event, the olefinically unsaturatedmonomer component must comprise at least one polyolefinicallyunsaturated monomer. As used herein "polyolefinically unsaturated" meanshaving at least two olefinic double bonds. The polyolefinicallyunsaturated monomers may be used in amounts of about 5% to about 30% andpreferably about 10% to 20% by weight of the composition.

Polyacrylates are generally useful, including 1,3-butylene glycoldiacrylate, diethylene glycol diacrylate, 1,6-hexanediol diacrylate,neopentylglycol diacrylate, polyethylene glycol diacrylate,tetraethylene glycol diacrylate, methylene glycol diacrylate,pentaerythritol tetraacrylate, tripropylene glycol diacrylate,ethoxylated bisphenol-A-diacrylate, trimethylolpropane triacrylate,di-trimethylolopropane tetraacrylate, dipenterythritol pentaacrylate,pentaerythritol triacrylate and the corresponding methacrylatecompounds. Also useful are reaction products of (meth)acrylic acid andepoxide resins, and urethane resins. Suitable poly(meth)acrylic estercompounds are also described in U.S. Pat. Nos. 4,051,195, 2,895,950,3,218,305, and 3,425,988.

Useful (meth)acrylic resins include esters and amides of (meth)acrylicacid as well as comonomers thereof with other copolymerizable monomers.Illustrative esters include methyl acrylate, methyl methacrylate,hydroxy ethyl acrylate, butyl methacrylate, octyl acrylate, and 2-epoxyethyl acrylate. Illustrative amides include bytoxymethyl acrylamide,methoacrylamide, and t-butyl acrylamide. Also suitable are copolymers ofsuch compounds, and copolymers with other monomers containingpolymerizable vinyl groups.

Another class of resins which are actinic radiation curable andpotentially suitable for use in the compositions in the inventioninclude vinyl monomers such as styrene, vinyl toluene, vinylpyrrolidone, vinyl acetate, divinyl benzene, and the like.

A further useful class of actinic radiation curable resin materialscomprises unsaturated polyesters, solubilized in vinyl monomers, asordinarily prepared from alpha-beta ethylenically unsaturatedpolycarboxylic acids and polyhydric alcohols, as described for examplein U.S. Pat. No. 4,025,407.

Particularly preferred polyolefinically unsaturated components includetrimethylolopropane trimethacrylate, trimethylolpropane triacrylate,dipentaerythritol pentaacrylate, pentaerythritol triacrylate,ethoxylated trimethylolpropane triacrylate, 1,6 hexanediol diacrylate,neopentyl glycol diacrylate, pentaerythritol tetraacrylate, and 1,3butylene glycol diacrylate. Preferred monoacrylates includecyclohexylacrylate, 2-ethoxyethyl acrylate, 2-methoxyethyl acrylate,benzoyl acrylate, and isobornylacrylate. Such compounds are availablefrom a variety of sources. For example, a preferred polyacrylate,dipentaerythritol monohydroxypentaacrylate is available as SR 399 fromSartomer Co.

It will be understood by those skilled in the art that the foregoinglisting of polyolefinically unsaturated compounds is intended only to beillustrative in character, and that any other resin compounds havingsuch functionality in their molecules and curable under actinicradiation conditions may potentially be employed. In addition to thosemonomers required to be present, other optional monomers may be presentwhich have both acrylate and epoxy functionality ("dual-functional"monomers).

As used herein, "actinic radiation" means electromagnetic radiationhaving a wavelength of about 700 nm or less which is capable, directlyor indirectly, of curing the specified resin component of the resincomposition. By indirect curing in this context is meant curing undersuch electromagnetic radiation conditions, as initiated, promoted, orotherwise mediated by another compound.

Accordingly, a non-peroxide photoinitiator is added to the compositionin an amount effective to respond to the actinic radiation and toinitiate and induce curing of the associated resin, via substantialpolymerization thereof.

Suitable photoinitiators useful with ultraviolet (UV) actinic radiationcuring mono- and polyolefinic monomers include free radical generatingUV initiators such as substituted benzophenones and substitutedacetophenones, benzoin and its alkyl esters and xanthone and substitutedxanthones. Preferred photoinitiators include diethoxy-acetophenone,benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether,diethoxyxanthone, chloro-thio-xanthone, azo-bisisobutyronitrile,N-methyl diethanol-amine-benzophenone and mixtures thereof.

Particularly preferred photoinitiators include2-hydroxy-2-methyl-1-phenyl-propan-1-one available as Darocur 1173 fromEM Industries, Inc., and 2-benzyl-2-(dimethylamino)-1-4-(4-morpholinyl)phenyl!-1-butanone available as Irgacure 369 fromCiba-Geigy.

The present invention requires the use of organic peroxides having 10hour decomposition half-lives (10 hr. T₂) at temperatures of from about50° C. to less than about 104° C. Peroxides having 10 hour decompositionhalf-lives at temperatures below this range do not yield compositionswhich have stable pot-life and shelf-life characteristics. Peroxideshaving 10 hour decomposition half-lives at temperatures above this rangehave not been found to be effective in preventing resin drip during theheat cure stage. The peroxides useful in the present invention are notuseful in themselves as photoinitiators.

These peroxides include various diacylperoxides such as diisononanoylperoxide, decanoyl peroxide, lauroyl peroxide, succinic acid peroxideand benzoyl peroxide.

Also useful are various peroxydicarbonates such asdi(n-propyl)peroxydicarbonate, di(sec-butyl)peroxydicarbonate, anddi(2-ethylhexyl)peroxydicarbonate.

Further useful peroxides include various peroxyesters such asα-cumylperoxyneodecanoate,1,1-dimethyl-3-hydroxy-butylperoxyneoheptanoate,α-cumylperoxyneoheptanoate, t-amyl-peroxyneodecanoate,t-butylperoxyneodecanoate, t-amyl-peroxypivalate, t-butylperoxypivalate,1-1-dimethyl-3-hydroxy-butylperoxy-2-ethylhexanoate,2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane,t-amylperoxy-2-ethylhexanoate, t-butylperoxy-2-ethylhexanoate,t-butylperoxyisobutyrate, t-butylperoxymaleic acid,t-butylperoxyacetate, t-amylperoxyacetate, t-amylperoxybenzoate,OO-t-butyl-O-isopropylmonoperoxycarbonate,2,5-dimethyl-2,5-di(benzoylperoxy)hexane,OO-t-butyl-O-(2-ethylhexyl)monoperoxycarbonate,OO-t-amyl-O-(2-ethylhexyl)monoperoxycarbonate.

In addition, certain peroxyketals are useful in the present inventionincluding 1,1-di(t-butylperoxy)-3,3,5-trimethyl cyclohexane,1,1-di(t-butylperoxy)cyclohexane, and 1,1-di(t-amylperoxy)cyclohexane.

Preferred organic peroxides include lauroyl peroxide, having a 10 hr.T_(1/2) of 64° C.; t-amylperoxy-2-ethylhexanoate, having a 10 hr.T_(1/2) of 75° C.; and 1,1-di(t-butylperoxy)-3,3,5-trimethylhexanehaving a 10 hr. T_(1/2) of 96° C. Lauroyl peroxide is available asAlperox-F; t-amylperoxy-2-ethylhexanoate is available as Lupersol 575;and 1,1-di(t-butylperoxy)-2,2,5-trimethylhexane is available as Lupersol256; all available from Elf Atochem North America, Inc.

Various conventional heat-activated curing agents for epoxies are usefulin the present invention including imidazoles, preferably2-ethyl-4-methyl imidazole,1-(2-cyanomethyl)-2-ethyl-α-4-methylimidazole and2-phenyl-4,5-dihydroxymethyl imidazole; aliphatic cycloaliphatic amines,preferably 2,2'-dimethyl-4,4'-methylene-bis(cyclohexylamine) (Ancamine2049); aromatic amines, preferably 4,4'-diaminodiphenyl sulfone(Ancamine S and Ancamine SP); a blend of aromatic and aliphatic amines(Ancamine 2038); dissociable amine salts; Lewis Acid catalysts such asboron trifluoride:amine complexes, preferably BF₃ :benzyl amine (Anchor1907), BF₃ :monoethyl amine (Anchor 1948) and liquid BF₃ :amine complex(Anchor 222); Lewis Base catalysts such as t-amines, preferablytris(dimethyl-aminomethyl)phenol (Ancamine K.54), dimethylaminomethylphenol (Ancamine 1110); dicyandiamides, preferably dicyandiamide(Amicure CG). The Ancamine, Anchor, and Amicure series are tradenamesfor heat activated curing agents marketed by Pacific Anchor PerformanceChemicals Division of Air Products and Chemicals, Inc.

Especially pertinent to the anhydride resin compositions of the presentinvention are the acid anhydride epoxy curing agents. These include,preferably, methyltetrahydrophthalic anhydride, methylhexahydrophthalicanhydride, chlorendic anhydride, and nadic methyl anhydride and mixturesthereof. Nadic methyl anhydride is available as AC-methyl fromAnhydrides and Chemicals, Inc.

It will be noted that anhydride based catalysis of epoxy polymerizationis an inherently slow process. Accordingly, the resin compositions ofthe present invention generally employ a minor amount of amineaccelerators of the anhydride catalysis, preferably benzyldimethylamine; 2-ethyl-4-methyl imidazole, available as Imicure EMI-24from Pacific Anchor; and 2,4-diamino-62'-methylimidazolyl-(1)'!ethyl-s-triazine isocyanurate adduct.

Other additives conventionally used in the art which do notsubstantially interfere with the objectives of the present invention maybe useful. Fillers, diluents, pigments, dyes, surface active agents,toughening agents, flame retardants and the like may be employed fortheir intended purposes.

The procedure for making the amine curing resin compositions of thepresent invention may be generally described as follows the epoxide,polyolefin, photoinitiator, and miscellaneous additives such asdefoaming agents, wetting agents and, optionally, fire retardants areblended together to obtain a homogeneous mixture. Peroxide is added andthe mixture is further stirred. The resin component and a heat activatedcuring agent such as ethylmethyl imidazole are then mixed in aproportion of about 17 parts of resin component to 1 part of the curingagent, stirred and deaerated under vacuum. The mixture is then ready forfilament winding or preparation of prepreg.

The procedure for making the anhydride compositions of the presentinvention may be generally described as follows: the resin component ismade by mixing the epoxide, polyolefin, photoinitiator, and additionalmiscellaneous components, such as defoaming agents, wetting agents and,optionally, fire retardants. This blend is stirred until the solution ishomogeneous, e.g., approximately 10 minutes. A peroxide is added and themixture is further stirred, e.g., for an additional 10 minutes. Theanhydride component comprises a mixture of an anhydride, such as nadicmethyl anhydride, and an anhydride accelerator, such asbenzyldimethylamine. This mixture is stirred until homogeneous,approximately 10 minutes. The resin and anhydride components are thenmixed in a proportion of about 1.6 parts of the resin component to 1part of the anhydride component. The mixture is then further stirred anddeaerated under vacuum. The composition is then ready for filamentwinding or for preparation of prepreg.

Consolidation of the adjacent layers into a unitary structure requiressufficient flow of the gelled resin during the heat-cure stage to meldthe adjacent filaments into an integral whole and produce a qualitypart. In cases where excessive UV exposure has been applied in anattempt to alleviate subsequent dripping, the acrylate matrix is toorigid to allow such flow to occur. On the other hand, if the acrylate isinsufficiently exposed to actinic radiation so as to create too soft agel, dripping during the heat-cure stage is inevitable. Theimmobilization of the resin by actinic radiation must produce alattice-like matrix that has sufficient gel structure to preventdripping prior to exposure to the heat cure stage. The organic peroxidethen completes the polymerization of any uncured olefinicallyunsaturated monomer during the heat cure stage to prevent resin drip.The immobilization must, however, allow for enough flowable character toallow the merger of the respective layers into a unitary mass, duringthe heat cure stage.

The following non-limiting examples are intended to further illustratethe present invention. Unless otherwise noted, amounts are given inweight percent of the total composition. Viscosities were determined bymeasuring 75 gram samples in a Brookfield DV I viscometer, using a 25°C. water bath.

EXAMPLE 1

Amine curing resin compositions (Compositions 1-4 set forth in Table Ibelow) were produced in accordance with the procedures of the presentinvention.

Filament wound articles were produced from the compositions using thegeneral methods described above. In particular, for Compositions 1-4,articles were produced using varying intensities and locations ofactinic light and varying winding speeds. Products were made using glassfiber and using carbon fiber.

Glass fiber articles were produced using two different winding speeds;12 inches/sec. and 20 inches/sec. At each speed, articles were producedwhich were exposed to one actinic radiation source, producing 120mW/cm², focused on the mandrel onto which the fiber was wound. Articleswere also produced, at each winding speed, which were exposed to tworadiation sources. The first exposure was to a 180 mW/cm² source as thefiber emerged from the resin bath. The second source was the 120 mW/cm²source at the mandrel as the fiber was wound. After winding, thesevarious articles were heat cured in an oven at 150° C. for two hours.Regardless of the winding speed and the number and location of actinicsources, the resins of the present invention exhibited no drip upon heatcure. Drip was assessed by collecting resin falling from the woundarticle onto a collector positioned beneath the article.

Carbon fiber articles were produced in similar fashion, using one or twoactinic sources. However, the intensities of the actinic radiation weregreater for the relatively UV-opaque carbon fiber windings than for therelatively UV-transmissive glass fiber windings. Specifically, thesource directed to the fiber on emerging from the resin bath was 450mW/cm² and the source focused on the mandrel was 250 mW/cm². Carbonfiber articles were produced at only one winding speed, i.e., 4inches/sec. Again, the articles were heat cured at 150° C. for twohours. Drip was observed in only one case, i.e., Composition 4.

As is evident from Table I, Compositions 1-4 are substantially identicalexcept for the particular peroxide used. It is apparent from the dripdata that the peroxides having a 10 hour T_(1/2) of less than 104° C.enable compositions which do not drip on heat-curing regardless of thefiber being used. Composition 4, employing t-butylperbenzoate with a 10hour T_(1/2) of 104° C., is useful on glass fiber, but is less desirablewhen applied to carbon fiber, as evidenced by observable drip.

                                      TABLE I                                     __________________________________________________________________________    AMINE CURING RESINS                                                                                   1      2     3     4                                                          wt. % (Phr**)                                                                        wt. % (Phr)                                                                         wt. % (Phr)                                                                         wt. % (Phr)                        __________________________________________________________________________    PART A                                                                        DIGLYCIDYL ETHER OF BISPHENOL A*                                                                      75  (100)                                                                            75 (100)                                                                            75 (100)                                                                            74.8                                                                             (100)                           NEOPENTYLGLYCOL DIACRYLATE                                                                            15  (20)                                                                             15 (20)                                                                             15 (20)                                                                             14.7                                                                             (20)                            HYDROXYMETHYLPHENYL PROPANONE                                                                         3   (4)                                                                              3  (4)                                                                              3  (4)                                                                              2.9                                                                              (4)                             LAUROYL PEROXIDE (64° C.)                                                                      0.8 (1)                                                                              --    --    --                                 T-AMYLPEROXY-2-ETHYL-HEXANOATE (75° C.)                                                        --     0.8                                                                              (1)                                                                              --    --                                 DI(t-BUTYLPEROXY) TRIMETHYL-                                                                          --     --    0.8                                                                              (1)                                                                              --                                 CYCLOHEXANE (96° C.)                                                   T-BUTYL PERBENZOATE (104° C.)***                                                               --     --    --    1.6                                                                              (2)                             DEFOAMING AGENT*        0.5 (0.7)                                                                            0.5                                                                              (0.7)                                                                            0.5                                                                              (0.7)                                                                            0.5                                                                              (0.7)                           WETTING AGENT*          0.1 (0.1)                                                                            0.1                                                                              (0.1)                                                                            0.1                                                                              (0.1)                                                                            0.1                                                                              (0.1)                           PART B                                                                        ETKYL METHYL IMIDAZOLE  5.6 (7.5)                                                                            5.6                                                                              (7.5)                                                                            5.6                                                                              (7.5)                                                                            5.4                                                                              (7.5)                           VISCOSITY (cps)                                                               0 HOUR                  730    860   1100  950                                2 HOURS                 1050   --    --    --                                 4 HOURS                 SOLID  --    --    --                                 8 HOURS                 SOLID  1690  1860  2030                               DRIP ON HOOP WIND                                                             GLASS FIBER             NO     NO    NO    NO                                 CARBON FIBER            NO     NO    NO    YES                                __________________________________________________________________________     *The diglycidyl ether of Bisphenol A used in this example was EPON 825,       available from Shell Chemical Co. The defoaming agent employed in the         various examples throughout this specification is a mixture of foam           destroying polymers and polysiloxanes. The wetting agent employed in the      examples herein is a fluorinated surfactant.                                  **parts per hundred                                                           ***10 hour halflife at 104° C.                                    

EXAMPLE 2

Anhydride curing resin compositions (Compositions 5-8 set forth in TableII below) were produced in accordance with the procedures of the presentinvention. As in Example 1 above, articles were made using glass andcarbon fibers coated with the anhydride curing resins. Glass fiberarticles were wound at 12 inches/sec. and at 20 inches/sec., and at eachwinding speed, articles were made using single and double irradiationsat the intensities as described in Example 1. Upon heat cure none of theresins were observed to drip.

Carbon fiber articles were also formed at a winding speed of 4inches/sec. using both single and double exposures to actinic radiation.The intensities of the UV light source were 450 mW/cm² on the fiber onemerging from the resin bath, and 250 mW/cm² on the fiber as it waswound on the mandrel. No drip was observed upon heat cure except forcarbon fiber articles made using Composition 8, in which the peroxidewas t-butyl perbenzoate.

As is evident from Table II, Compositions 5-8 are substantiallyidentical except for the particular peroxide used. As with the aminecuring resin compositions described above in Table I, it is apparentfrom the drip data that peroxides having a 10 hour T_(1/2) of less than104° C. enable anhydride curing compositions to be formulated which donot drip on heat-curing. As was the case in Example 1 above, Composition8, a resin containing t-butylperbenzoate, when applied to UV-opaquecarbon fiber, dripped during heat cure.

                                      TABLE II                                    __________________________________________________________________________    ANHYDRIDE CURING RESINS                                                                           5      6     7     8                                                          wt. % (Phr***)                                                                       wt. % (Phr)                                                                         wt. % (Phr)                                                                         wt. % (Phr)                            __________________________________________________________________________    PART A                                                                        DIGLYCIDYL ETHER OF BISPHENOL A                                                                   42.9                                                                              (100)                                                                            42.9                                                                             (100)                                                                            42.9                                                                             (100)                                                                            42.8                                                                             (100)                               TMPTMA*             14.5                                                                              (34)                                                                             14.5                                                                             (34)                                                                             14.5                                                                             (34)                                                                             14.4                                                                             (34)                                HYDROXYMETHYLPHENYL PROPANONE                                                                     2.2 (5)                                                                              2.2                                                                              (5)                                                                              2.2                                                                              (5)                                                                              2.1                                                                              (5)                                 LAUROYL PEROXIDE (64° C.)**                                                                0.4 (1)                                                                              --    --    --                                     T-AMYLPEROXY-2-ETHYL-                                                                             --     0.4                                                                              (1)                                                                              --    --                                     HEXANOATE (75° C.)**                                                   DI(t-BUTYLPEROXY)   --     --    0.4                                                                              (1)                                                                              --                                     TRIMETHYLCYCLOHEXANE (96° C.)**                                        T-BUTYL PERBENZOATE (104° C.)**                                                            --     --    --    0.8                                                                              (2)                                 DEFOAMING AGENT     0.6 (1.4)                                                                            0.6                                                                              (1.4)                                                                            0.6                                                                              (1.4)                                                                            0.6                                                                              (1.4)                               WETTING AGENT       0.1 (0.2)                                                                            0.1                                                                              (0.2)                                                                            0.1                                                                              (0.2)                                                                            0.1                                                                              (0.2)                               PART B                                                                        NADIC METHYL ANHYDRIDE                                                                            38.7                                                                              (90)                                                                             38.7                                                                             (.90)                                                                            38.7                                                                             (90)                                                                             38.6                                                                             (90)                                BENZYL DIMETHYL AMINE                                                                             0.6 (1.4)                                                                            0.6                                                                              (1.4)                                                                            0.6                                                                              (1.4)                                                                            0.6                                                                              (1.4)                               VISCOSITY (cps)                                                                0 HOUR             650    1086  750   800                                    24 HOURS            1700   1416  1700  2100                                   48 HOURS            1700   2846  2000  2300                                   DRIP ON HOOP WIND                                                             GLASS FIBER         NO     NO    NO    NO                                     CARBON FIBER        NO     NO    NO    NO                                     __________________________________________________________________________     *TMPTMA is an abbreviation for trimethylolpropane trimethacrylate.            **Indicates 10 hour T.sub.1/2  temperature.                                   ***parts per hundred                                                     

EXAMPLE 3

Resin compositions formulated in accordance with the procedures setforth herein are described in Table III. Composition 9 is representativeof an amine curing resin of the present invention. Composition 10 isrepresentative of Example 2 of U.S. Pat. No. 4,092,443 to Green.Composition 11 is representative of the amine curing resin of thepresent invention, but without an organic peroxide.

                  TABLE III                                                       ______________________________________                                                       9             10        11                                                    wt.    ***    wt.       wt.                                    MATERIALS      %      (Phr)  %    (Phr)                                                                              %    (Phr)                             ______________________________________                                        2,2-BIS        --            47.2 (100)                                                                              --   (100)                             (GLYCIDYLOXYPHENYL)                                                           PROPANE*                                                                      DIGLYCIDYLETHER OF                                                                           74.4   (100)  --        75.5 (100)                             BISPHENOL A**                                                                 ETHYL METHYL   5.6    (7.5)  --        5.7  (7.5)                             IMIDAZOLE                                                                     DICYANDIAMIDE  --            3.7  (7.8)                                                                              --                                     NEOPENTYL GLYCOL                                                                             14.9   (20)   47.2 (100)                                                                              15.1 (20)                              DIACRYLATE                                                                    T-AMYLPEROXY-2-                                                                              1.5    (2)    --        --                                     ETHYLHEXANOATE                                                                HYDROXYMETHYL- 3      (4)    --        3.1  (2)                               PHENYL                                                                        PROPANONE                                                                     BENZYL DIMETHYL                                                                              --            1.9  (4)  --                                     ACETAL                                                                        DEFOAMING AGENT                                                                              0.5    (0.7)  --        0.5  (0.7)                             WETTING AGENT  0.1    (0.1)  --        0.1  (0.1)                             ______________________________________                                         *EPON 828 from Dow Chemical Co.                                               **EPON 825 from Dow Chemical Co.                                              ***Parts Per Hundred                                                     

The compositions were then used in a filament winding process inaccordance with the procedures described herein. These results aretabulated in Table IV, below. This process was conducted using fibersmade from glass and graphite, respectively, with each composition beingapplied to each kind of fiber in separate preparations. In addition, asfor previous Examples, two winding speeds were examined; 12 inches/sec.and 20 inches/sec. The coated fibers were first gelled by exposure to UVlight at an intensity of 120 mW/cm² as they were wound around a mandrel,and then placed in an oven for heat curing for 2 hours at a temperatureof 150° C. The resin was then observed for evidence of dripping and forquality of part consolidation (Table IV). Contrary to customary practicefor dual-curing filament processes, no rotation of the parts in the ovenwas performed. Rotation is conventionally required to compensate forexcessive resin flow during heating which creates drip and non-uniformdistribution of the resin on the fiber substrate.

                                      TABLE IV                                    __________________________________________________________________________             9         10        11                                                        GLASS                                                                             GRAPHITE                                                                            GLASS                                                                             GRAPHITE                                                                            GLASS                                                                             GRAPHITE                                     __________________________________________________________________________    WINDING SPEED = 12 in./sec.                                                   PART     GOOD                                                                              GOOD  POOR                                                                              GOOD  GOOD                                                                              GOOD                                         CONSOLIDATION                                                                 DRIP DURING                                                                            NO  NO    YES YES   NO* YES                                          HEAT CURE                                                                     WINDING SPEED = 20 in./sec.                                                   PART     GOOD                                                                              --    POOR                                                                              --    GOOD                                                                              --                                           CONSOLIDATION                                                                 DRIP DURING                                                                            NO  --    YES --    NO  --                                           HEAT CURE                                                                     __________________________________________________________________________     *At these winding speeds, the transparency of the glass fibers allows for     sufficient immobilization of the composition in the absence of a peroxide     to prevent resin drip. This is not true for more opaque fibers such as        graphite and at very fast winding speeds.                                

Composition 9, representing the amine curing resin of the presentinvention, was found to be free of drip and maintained uniformity ofresin distribution throughout the substrate layers.

Composition 10, representative of those exemplified in theabove-mentioned patent to Green, was found not to be useful for windingapplications in accordance with the present invention. The results ofthe heat-cure demonstrated observable dripping and loss of uniformity inthe resin distribution. The Green composition does not employ peroxidesin accordance with the present invention. Instead, Green uses benzyldimethyl acetal, described as a photopolymerization catalyst.

Composition 11 is representative of a composition similar to the aminecuring resin of the present invention, but lacking the peroxide. Thiscomposition is also similar to Green in that it also contains animidazole. The resin without peroxide exhibited variable results, asshown in Table IV above. When applied to graphite fiber, Composition 11showed significant resin drip upon heat cure. However, when applied toglass fiber, at winding speeds of both 12 and 20 in./sec., the resinprovided good part consolidation and no significant resin drip upon heatcure. It is believed that at these winding speeds the glass fibertransmits sufficient UV light for the resin to gel sufficiently toprevent drip even in the absence of the peroxide. But the compositionwithout a peroxide is not effective as an amine curing resin for theimpregnation of UV-opaque fibers, such as carbon black or at very fastwinding speeds on glass.

Compositions 4 (Example 1) and 8 (Example 2), employing t-bury1perbenzoate with a T_(1/2) of 104° C., demonstrate performancesubstantially comparable to Composition 11 having no peroxide at all.These compositions are less effective for applications involvingUV-opaque fiber, such as carbon fiber, and they are therefore lessdesirable. It is apparent from these experiments that the presence ofperoxides having the requisite 10 hour T_(1/2) of less than 104° C.enable the creation of a filament wound composite which has non-dripcapability during the heat-cure stage.

The present inventive compositions can be used on virtually any type offiber, whereas compositions such as those disclosed by Green and thoseof Composition 11 above many work without dripping only provided thetransparencey of the fibers and the winding speed is sufficient toprevent drip. However, such compositions cannot lead to any practical orpredictable commercial use for non-drip requirements.

EXAMPLE 4

Table V, below, summarizes a comparison of the viscosities of the resinsof the present invention (Compositions 13 and 14) against the viscosityof a resin described by the aforementioned Drain et al. patent(Composition 12). The viscosities of Compositions 12-14 were determinedby measuring the viscosity of 75 gram samples of each composition on aBrookfield DV I viscometer, using a 25° C. water bath. The two resinexamples of the present invention retain commercially useful lowviscosities, i.e., <2000 cps, for at least eight hours at ambient lightand temperature, while the Drain et al. composition becomes unworkablewithin two hours. It is apparent therefore that the compositions of thepresent invention possess the significant advantage of relatively longpot-life. A long resin pot-life is desirable for practical industrialuse since it can eliminate the need for two component mixing/meteringmachines and their associated clean up and maintenance problems.

Table V, below, also provides a comparison of the glass transitiontemperatures (T_(g) ) of the resin compositions of the present invention(Compositions 13 and 14) with that of a resin of the Drain et al. patent(Composition 12). Compositions 13 and 14 have T_(g) s of 120° C. and152° C., respectively, while Composition 12 has a T_(g) of 80° C. Thehigher glass transition temperatures of the compositions of the presentinvention provide greater temperature resistance when used in fibercomposite articles, and unlike the resins of Drain et al., are useful inhigher temperature applications.

                                      TABLE V                                     __________________________________________________________________________                        12      13      14                                                            DRAIN ET AL.                                                                          AMINE CURING                                                                          ANHYDRIDE CURING                                              RESIN   RESIN   RESIN                                                         PER     PHR     PHR                                       __________________________________________________________________________    EPOXY MATERIALS                                                               2,2-BIS(GLYCIDYLOXYPHENYL)                                                                        100             100                                       PROPANE*                                                                      DIGLYCIDYL ETHER OF --      100     --                                        BISPHENOL A*                                                                  CYCLOALIPHATIC EPOXIDE*                                                                           --      --      18                                        ACRYLATE MATERIALS                                                            DPMP*               20      --      21                                        HEXANEDIOL DIACRYLATE                                                                             --      20      10                                        HYDROXYPROPYL METHACRYLATE                                                                        --      --      12                                        T-BUTYL PERBENZOATE 2       2       2                                         HYDROXYMETHYLPHENYL PROPANONE                                                                     1       4       5                                         DIAMINO POLYPROPYLENE OXIDE*                                                                      20      --      --                                        ETHYL METHYL IMIDAZOLE                                                                            --      7.5     0.5                                       NADIC METHYL ANHYDRIDE                                                                            --      --      124                                       VISCOSITY (cps)                                                                0 HOUR             960     660     640                                        2 HOURS            10,000  --      --                                         8 HOURS            260,000 1270    --                                        24 HOURS            SOLID   3610    1070                                      Tg(°C.)      80      120     152                                       __________________________________________________________________________     *The 2,2bis(glycidyloxyphenyl) propane used in for Examples 12-14 was EPO     828 available from Shell Chemical Co. The diglycidyl ether of Bisphenol A     was EPON 825 also available from Shell Chemical Co. The cycloaliphatic        epoxide used was ERL4221 available from Union Carbide Co. DPMP is an          abbreviation for dipentaerythritol monohydroxy pentaacrylate. The diamino     polypropylene oxide used in the examples was Jeffamine D230 available fro     Texaco. EPON 828 and 825 are oligomers of each other.                    

EXAMPLE 5 EXPERIMENTAL

To further clarify how the resin composition of the invention may bedistinguished over the compositions disclosed in the cited prior art,the following experiments were performed. Three resin compositions wereprepared. Two of the compositions were prepared using compositions whichwere representative of the prior art, containing either a photoinitiator(Composition A) or an organic peroxide (Composition B). The thirdcomposition was prepared to be representative of the compositions of theinvention, and thus contained both a photoinitiator and lauroylperoxide, a heat-activated peroxide (Composition C). Each of thesecompositions is described in detail in Table VI below. The compositionsdescribed in Table VI were each employed in a series of filament windingtrials. The results are summarized in Table VII.

                  TABLE VI                                                        ______________________________________                                                        A          B      C                                           COMPOSITION     PHR        PHR    PHR                                         ______________________________________                                        DIGLYDICYL ETHER OF                                                                           100        100    100                                         BISPHENOL A                                                                   (Epoxy Equivalent                                                             Weight - 172-178)                                                             2-ETHYL-4-METHYL                                                                              7.5        7.5    7.5                                         IMIDAZOLE                                                                     NEOPENTYL GLYCOL                                                                              20         20     20                                          DIACRYLATE                                                                    DAROCURE ® 1173*                                                                          4          --     4                                           (PHOTOINITIATOR)                                                              ® Ciba-Geigy Corp.                                                        LAUROYL PEROXIDE                                                                              --         1      1                                           070 ®       0.7        0.7    0.7                                         (DEFOAMING AGENT)                                                             ® Byk-Chemie                                                              FLUARAD ™ FC-430                                                                           0.1        0.1    0.1                                         (WETTING AGENT)                                                               ™ 3M Corp.                                                                 ______________________________________                                         *DAROCURE ®1173 = 2hydroxy-2-methyl-1-phenyl-propan-one              

                  TABLE VII                                                       ______________________________________                                        WINDING EXPERIMENTS                                                           FIBER                                                                         WINDING     GLASS         GRAPHITE                                            (in/sec)    5      10      20   5     10   20                                 ______________________________________                                        PRIOR ART COMPOSITION A                                                       DRIP DURING NO     NO      NO   NO    NO   NO                                 UV CURE                                                                       DRIP DURING NO     NO      NO   YES   YES  YES                                HEAT CURE                                                                     % RESIN DRIP                                                                              0      0       0    8     7    9                                  PRIOR ART COMPOSITION B                                                       DRIP DURING YES    YES     YES  YES   YES  YES                                UV CURE                                                                       DRIP DURING YES    YES     YES  YES   YES  YES                                HEAT CURE                                                                     % RESIN DRIP                                                                              10     11      12   4     9    9                                  PRIOR ART COMPOSITION C                                                       DRIP DURING NO     NO      NO   NO    NO   NO                                 UV CURE                                                                       DRIP DURING NO     NO      NO   NO    NO   YES                                HEAT CURE                                                                     % RESIN DRIP                                                                              0      0       0    0     0    1                                  ______________________________________                                    

Each of the compositions was employed to produce filament wound productsusing glass and graphite fibers. Various winding speeds, i.e., five,ten, and twenty inches per second, were employed. The products wereobserved for resin drip during the ultraviolet light (UV) cure stage aswell as during the heat cure stage. In addition, the total percent resindrip after heat cure was measured. During each of the experiments, theintensity of the ultra-violet light employed during the UV cure stagewas 90 mw/cm². In addition, the temperature employed during the heatcure stage was 177° C.

The results of the filament winding trials clearly demonstrate that theresin composition of the invention effectively eliminates resin dripduring filament winding processes, and is, therefore, distinguishableover the compositions known in the prior art. While prior artComposition A did not show drip during UV or heat cure with glassfibers, which are somewhat transparent to UV light, it did showsignificant drip from graphite fibers, which are not transparent to UVlight, during the heat cure stage of the filament winding trials,resulting in between 7% and 10% total resin loss. Prior art CompositionB was even less effective, producing significant resin drip during boththe heat cure and UV cure stages using either glass or graphite fibers.Total resin loss varied between 4% and 12% after heat cure.

In contrast, the Composition representative of the present invention,i.e., Composition C, showed virtually no measurable resin drip,regardless of fiber type. One exception to this was a 1% resin loss ongraphite fibers at the very highest winding speed. This loss wasvirtually insignificant.

Further experiments were performed to demonstrate that organic peroxidescannot function as photoinitiators. Thus, the chemical functionsperformed by the photoinitiator and the heat-activated peroxidesemployed in the compositions of the invention are distinct and do notoverlap.

These experiments were performed by testing samples of each compositionin a DPC 930 differential photocalorimeter from TA Instruments ofWilmington, DE. Differential photocalorimetry is a specialized extensionof differential scanning calorimetry designed to measure temperaturesand heat flow resulting from photoinitiated reactions and transitions.These techniques are well understood and used in the art or polymerchemistry.

Three measurements which are indicative of photoinitiator capability areenthalpy of reaction, induction time, and time to peak maximum. Usingthis apparatus, each of these parameters was measured for eachcomposition. The "enthalpy" of the reaction is the actual heat ofreaction calculated, in joules per gram (J/g), from the polymerizationof the sample. The "induction time" is the time, in seconds, between theopening of the apparatus shutter and the point at which the reaction is1% complete. The "time to peak maximum" is the time, in seconds, fromthe shutter opening to the point when the heat flow curve of thereaction reaches its maximum value. These terms are well known in theart of the polymer chemistry and differential scanning calorimetry, andare consistent with the usages found in the Analysis Manual of the DPC930 apparatus.

The results of these experiments are illustrated in Table VIII below.

                  TABLE VIII                                                      ______________________________________                                        DIFFERENTIAL PHOTOCALORIMETRY EXPERIMENTS                                              D    E      F      G     H    I    J                                          PHR  PHR    PHR    PHR   PHR  PHR  PHR                               ______________________________________                                        COMPOSITION                                                                   EPON 825.sup.1                                                                           100    100    100  100   100  100  100                             2-ETHYL-4- 7.5    7.5    7.5  7.5   7.5  7.5  7.5                             METHYL                                                                        IMIDAZOLE                                                                     NPGDA.sup.2                                                                              20     20     20   20    20   20   20                              DAROCURE 1173.sup.3                                                                      4      --     4    --    4    --   4                               LAUROYL    --     1      1    --    --   --   --                              PEROXIDE                                                                      LUPERSOL 575.sup.4                                                                       --     --     --   1     1    --   --                              LUPERSOL 231.sup.5                                                                       --     --     --   --    --   1    1                               DPC DATA                                                                      ENTHALPY (J/g)                                                                           78     58     77   0     82   0    72                              INDUCTION TIME                                                                           4      33     3    0     3    0    3                               (sec)                                                                         TIME To PEAK                                                                             9      58     7    0     8    0    8                               MAX. (sec)                                                                    ______________________________________                                         .sup.1 EPON 825 = Diglycidyl Ether of Bisphenol A.                            .sup.2 NPGDA = Neopentyl Glycol Diacrylate.                                   .sup.3 Darocure 1173 = 2Hydroxy-2-nethyl-1-phenyl-propan-1-one.               .sup.4 Lupersol 575 = tAmylperoxy-2-ethylhexanoate.                           .sup.5 Lupersol 231 = 1,1DI(t-butylperoxy) 3,3,5trimethylcyclohexane.    

Composition D, illustrative of the compositions of the prior art,contained only a photoinitiator, i.e., Darocure 1173. The enthalpy ofthe reaction was 78 J/g, with an induction time of 4 seconds and a timeto peak maximum of 9 seconds. These results are typical ofphotoinitiators used to initiate photopolymerizations. Typically, tofunction as a commercially viable photoinitiator, the enthalpy ofreaction must be relatively high, and induction and peak maximum timesmust be as low as possible. That is, energy absorption and consequentfree radical generation must be efficient; intense absorption in a shortamount of time. Materials which do not give such results are generallynot useful as photoinitiators.

To illustrate that a peroxide alone does not give enthalpy or inductionor peak times corresponding to photoinitiators, each of three differentperoxides was tested, alone and in combination with the samephotoinitiator, in a series of experiments to determine the capacity ofeach of the peroxides to catalyze a photochemical reaction. In each ofCompositions E, G, and I, a heat-activated peroxide was employed in theabsence of a photoinitiator. Compositions 2, 4, and 6 either produced nomeasurable photochemical reaction or, in the case of lauroyl peroxide,induction and peak maximum times too long for practical use as aphotoinitiator in filament winding compositions, as demonstrated by theexperiments with Composition B in Tables VI and VII.

These results are further emphasized by Composition F, which contained acombination of the photoinitiator and lauroyl peroxide. The enthalpy,induction time, and time to peak maximum for this composition arevirtually identical to that for Composition D containing thephotoinitiator alone. This illustrates that the lauroyl peroxide doesnot substantially participate in the photochemical cure of the resincompositions. This is also true with regard to other heat-activatedperoxides used in combination with the photoinitiator, i.e. CompositionsH and J.

Example 6

This example is intended to demonstrate, using thermogravimetricanalysis, that the compositions and processes of the present inventionallow for non-drip properties during heat cure. Through the use ofthermogravimetric analysis, the uniformity of resin distribution can bedetermined, thereby evidencing the non-drip feature.

The data shown in Table IX are the results of a comparison of twofilament windings using an amine curing resin composition of the presentinvention. The amine curing composition was prepared according to theprocedures described herein using 74.4 wt. % diglycidyl ether ofBisphenol A, 5.6 wt. % ethyl methyl imidazole, 14.9 wt. % neopentylglycol diacrylate, 1.5 wt. % t-amylperoxy-2-ethyl-hexanoate, 3.0 wt. %2-benzyl-2-methyl-1-phenyl-propan-1-one, along with 0.5 wt. % defoamingagent and 0.1 wt. % wetting agent. Filament winding was performed ingeneral accordance with the procedures described above. Fiberglass wasimpregnated at a speed of 12 in./sec. and formed into articles bywinding onto two separate mandrels. One winding was exposed to UV lightat an intensity of 120 mW/cm². Another winding was not exposed to UVlight. Both articles were heat-cured without rotation for 2 hours at150° C.

                  TABLE IX                                                        ______________________________________                                                          UV    HEAT                                                                    HEAT  ONLY                                                  ______________________________________                                        RESIN WT. % - TOP   25.7    24.7                                              RESIN WT. % - BOTTOM                                                                              25.6    30.0                                              DRIP                NO      YES                                               ______________________________________                                    

The data in Table IX are the results of thermogravimetric analysis (TGA)of the heat-cured articles. TGA was performed in accordance with theprinciples described in W. W. Wendlandt and P. K. Gallagher,"Instrumentation", Chapter 1 of Thermal Characterization of PolymericMaterials, E. A. Turi, ed., Academic Press, 1981.

The resultant articles were then subjected to thermogravimetric analysisfor determination of uniformity of resin distribution. Sections of thetop and bottom of the wound article were cut off, weighed, and theweighed samples then heated slowly to a temperature of 800° C., atemperature sufficient to burn off the resin coating leaving the heatresistant fiber behind. During the heating process, the samples weightsare monitored by the instrument. The final difference in the weights ofthe sample before and after heating, provides a measure of the quantityof resin present in the sample. Uniformity of resin distribution isindicated if the resin proportion of each sample is substantiallyidentical. If a substantial difference in sample weights is observed,then the resin is deemed to have been distributed non-uniformly on thearticle due to excessive resin flow and drip during heat cure.

If desired, the uniformity of the coating of the resin onto the fibermay be determined prior to winding of the coated fiber onto a mandrel.However, it will be noted by those having skill in the art that anyinitial irregularity or non-uniformity of resin coating on the fiberwill not affect the uniformity of the wound article because of theability of the gelled resin to flow and merge with overlapping resinduring winding onto the mandrel.

Samples were taken from the top and bottom portions of each article. TheTGA results show that the article initially cured by UV exposureretained uniform resin distribution without the necessity for rotatingthe part during the heat-cure step. Furthermore, no resin drip wasobserved on the UV cured article. The data also show that in the absenceof UV exposure the resin will flow from the top portion of the articleto the bottom, and that the resin will also drip during the heat-cure.The article will thereby become substantially anisotropic.

EXAMPLE 7

A further example of the anhydride curing compositions of the presentinvention is shown below in Table X. Fiberglass articles made using thiscomposition were UV cured and then heat cured, preferably by heating at170° C. for 1 hour.

                  TABLE X                                                         ______________________________________                                                              WT. % (Phr)                                             ______________________________________                                        RESIN COMPONENT                                                               DIGLYCIDYL ETHER OF BISPHENOL A                                                                       57.47   100                                           CYCLOALIPHATIC EPOXIDE* 11.77   21                                            MODIFIED DIGLYDICYL ETHER OF                                                  BISPHENOL A*            9.98    17                                            DPMP*                   10.21   18                                            HYDROXYPROPYL METHACRYLATE                                                                            3.31    6                                             T-BUTYL PERBENZOATE     1.19    2                                             WETTING AGENT           0.12    0.2                                           METHYL IMIDAZOLE        5.85    10                                            TOTAL                   100.00                                                ANHYDRIDE COMPONENT                                                           NADIC METHYL ANYDRIDE   98.92   172                                           PHOTOINITIATOR          1.08    2                                             TOTAL                   100.00                                                ______________________________________                                         *In Table VII, the cycloaliphatic epoxide used was ERL 4221 available fro     Union Carbide Co. The modified diglydidylether of Bisphenol A was EPIREZ      5027 available from Rhone Poulenc. DPMP is an abbreviation for                dipentaerythritol monohydroxy pentacrylate. The photoinitiator used was       2benzyl-2-dimethylamino-1- 4-(4- morpholinyl)phenyl!-1butananone.        

EXAMPLE 8

A most preferred embodiment of the present invention has the followingcomposition:

    ______________________________________                                        PART A                     Phr                                                ______________________________________                                        Bisphenol F/Epichlorohydrin based                                                                        50                                                 Epoxy Resin                                                                   Bisphenol A/Epichlorohydrin based                                                                        50                                                 Epoxy Resin                18                                                 Isobornyl Acrylate         18                                                 Butanediol Diacrylate      5                                                  Propoxylated Neopentyl Glycol Diacrylate                                                                 5                                                  1-Phenyl-2-Hydroxy-2-Methylpropan-1-one                                                                  4                                                  1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane                                                         0.3                                                Defoaming Agent            0.66                                               Wetting Agent              0.13                                               PART B                                                                        1-(2-hydroxypropyl) Imidazole                                                                            4                                                  ______________________________________                                    

The use of the Bisphenol F/Epichlorohydrin based epoxy resin, which doesnot crystallize over time at room temperature, is advantageous in thepresent invention. The use of noncrystallizing epoxies are thereforepreferred and particularly when blended with epoxies which have atendency to crystallize at room temperature, such as Bisphenol A.Additionally, it is important to the integrity and quality of the finalcomposite that azo compounds which result in nitrogen bubbles not beused in the composition as the peroxide heat curing agent.

While the invention has been described with reference to specificembodiments, it will be apparent that numerous variations, modificationsand embodiments are possible, and accordingly all such variations,modifications and embodiments are to be regarded as being within thespirit and scope of the present invention.

What is claimed is:
 1. A method of preparing a filament windingfiber/resin composite substantially free of resin drip comprising:a)providing a stable liquid resin composition comprising:i. an epoxycomponent including at least one polyepoxide resin curable by heat; ii.at least one heat activated curing agent for said epoxy component; iii.an olefinically unsaturated monomer component including at least onepolyolefinically unsaturated monomer curable by actinic radiation; iv.at least one photoinitiator which is not a peroxide; and v. at least oneheat activated organic peroxide for said olefinically unsaturatedmonomer component, said peroxide having a ten hour decompositionhalf-life at temperatures from about 50° C. to less than about 104° C.and which is substantially unreactive in the presence of actinicradiation and in the absence of a photosensitizer; b) applying saidresin composition to a fiber to form a fiber/resin composite; c)subjecting said fiber/resin composite to actinic radiation sufficient toimmobilize said resin composition by at least partially curing saidolefinically unsaturated monomer; and d) subjecting said fiber/resincomposite to heat sufficient to activate said organic peroxide to cureremaining unreacted olefinically unsaturated monomer and immobilize saidresin composition and to cure said polyepoxide; wherein saidimmobilization with actinic radiation and further heat-curing occurswithout substantial resin drip and yields a T_(g) of at least about 110°C.
 2. The method of claim 1 wherein the organic peroxide is selectedfrom the group consisting of diacylperoxides, peroxydicarbonates,peroxyesters, and peroxyketals and mixtures thereof.
 3. The method ofclaim 2 wherein the organic peroxide is selected from the groupconsisting of lauroyl peroxide, t-amylperoxy-2-ethylhexanoate and1,1-di(t-butylperoxy)-3,3,5-trimethylhexane.
 4. The method of claim 1wherein the organic peroxide is included in an amount of from about 0.2wt. % to about 2 wt. %.
 5. The method of claim 4 wherein the organicperoxide is included in an amount of from about 0.5 wt. % to about 1.5wt. %.
 6. The method of claim 1 wherein the polyepoxide resin isselected from the group consisting of polyglycidyl andpoly(β-methylglycidyl)ethers of dihydric and polyhydric alcohols andphenols, novolaks, alkyl-substituted phenols and halogen-substitutedphenols, poly(N-glycidyl) compounds obtained from amines containing atleast two amino-hydrogen atoms, triglycidylisocyanurate, N,N'-diglycidylderivatives of cyclic alkaline ureas and hydantoins, poly(S-glycidyl)derivatives of dithiols and mixtures thereof.
 7. The method of claim 6wherein the polyepoxide resin is selected from the group consisting ofdiglycidyl ethers of bisphenols.
 8. The method of claim 1 wherein theepoxy component is included in an amount of from about 60 wt. % to about85 wt. %.
 9. The method of claim 8 wherein the epoxy component isincluded in an amount of from about 63 wt. % to about 75 wt. %.
 10. Themethod of claim 1 wherein the polyolefinically unsaturated monomer isselected from the group consisting of acrylic and methacrylic resins,vinyl monomers, unsaturated polyesters solubilized in vinyl monomers andmixtures thereof.
 11. The method of claim 10 wherein thepolyolefinically unsaturated monomer is selected from the groupconsisting of trimethylolopropane trimethacrylate, trimethylolpropanetriacrylate, dipentaerythritol monohydroxypentaacrylate, pentaerythritoltriacrylate, ethoxylated trimethylolpropane triacrylate, 1,6-hexanedioldiacrylate, neopentyl glycol diacrylate pentaerythritol tetraacrylate,and 1,3-butylene glycol diacrylate.
 12. The method of claim 1 whereinthe polyolefinically unsaturated monomer is included in an amount offrom about 5 wt. % to about 30 wt. %.
 13. The method of claim 12 whereinthe polyolefinically unsaturated monomer is included in an amount offrom about 10 wt. % to about 20 wt. %.
 14. The method of claim 1 whereinthe photoinitiator is selected from the group consisting of substitutedbenzophenones, substituted acetophenones, benzoin and its alkylethers,xanthone and substituted xanthones and mixtures thereof.
 15. The methodof claim 14 wherein the photoinitiator is selected from the groupconsisting of 2-hydroxy-2-methyl-1-phenyl-propan-1-one and2-benzyl-2-(dimethylamino)-1- 4-(4-morpholinyl)phenyl!-1-butanone. 16.The method of claim 1 wherein the photoinitiator is included in anamount of from about 1 wt. % to about 10 wt. %.
 17. The method of claim16 wherein the photoinitiator is included in an amount of from about 2wt. % to about 5 wt. %.
 18. The method of claim 16 wherein the heatactivated curing agent is selected from the group consisting ofdicyandiamides, boron trifluoride:amine complexes, borontrichloride:amine complexes, latent amine curatives, tertiary amines andaromatic polyamines, dissociable amine salts imidazoles and mixturesthereof.
 19. The method of claim 18 wherein the heat activated curingagent is selected from the group consisting of2-ethyl-4-methylimidazole, 1-(2-cyanoethyl)-2-ethyl-α-4-methylimidazoleand 2-phenyl-4,5-dihydroxymethyl imidazole.
 20. The method of claim 1wherein the heat activated curing agent is included in an amount of fromabout 2 wt. % to about 10 wt. %.
 21. The method of claim 20 wherein theheat activated curing agent is included in an amount of from about 3 wt.% to about 6 wt. %.
 22. The method of claim 1 wherein said viscosityremains from about 300 centipoise to about 2,000 centipoise for aminimum of about 6 hours at a temperature of from about ambienttemperature to about 60° C.
 23. A method of preparing a filament windingfiber/resin composite substantially free of resin drip comprising:a)providing a stable liquid resin composition comprising:i. an epoxycomponent including at least one polyepoxide resin curable by heat; ii.at least one heat activated curing agent for said epoxy componentcomprising at least one carboxylic acid anhydride and at least oneanhydride accelerator; iii. an olefinically unsaturated monomercomponent including at least one polyolefinically unsaturated monomercurable by actinic radiation; iv. at least one photoinitiator which isnot a peroxide; and v. at least one heat activated organic peroxide forsaid olefinically unsaturated monomer component, said peroxide having aten hour decomposition half-life at temperatures from about 50° C. toless than about 104° C. and which is substantially unreactive in thepresence of actinic radiation and in the absence of a photosensitizer;b) applying said resin composition to a fiber to form a fiber/resincomposite; c) subjecting said fiber/resin composite to actinic radiationsufficient to immobilize said resin composition by at least partiallycuring said olefinically unsaturated monomer; and d) subjecting saidfiber/resin composite to heat sufficient to activate said or organicperoxide to cure remaining unreacted olefinically unsaturated monomerand immobilize said resin composition and to cure said polyepoxide;wherein said immobilization with actinic radiation and furtherheat-curing occurs without substantial resin drip and yields a T_(g) ofat least about 110° C.
 24. The method of claim 23 wherein the organicperoxide is selected from the group consisting diacylperoxides,peroxydicarbonates, peroxyesters, peroxyketals and mixtures thereof. 25.The method of claim 23 wherein the organic peroxide is selected from thegroup consisting of lauroyl peroxide, t-amylperoxy-2-ethylhexanoate and1,1-di(t-butylperoxy)-3,3,5-trimethylhexane.
 26. The method of claim 23wherein the organic peroxide is included in an amount of from about 0.2wt. % to about 2 wt. %.
 27. The method of claim 26 wherein the organicperoxide is included in an amount of from about 0.3 wt. % to about 1.0wt. %.
 28. The method of claim 23 wherein the polyepoxide resin isselected from the group consisting of polyglycidyl andpoly(β-methylglycidyl)ethers of dihydric and polyhydric alcohols andphenols, novolaks, alkyl-substituted phenols and halogen-substitutedphenols, poly(N-glycidyl) compounds obtained from amines obtained fromamines containing at least two amino-hydrogen atoms,triglycidylisocyanurate, N,N'-diglycidyl derivatives of cyclic alkalineureas and hydantoins, poly(S-glycidyl) derivatives of dithiols andmixtures thereof.
 29. The method of claim 28 wherein the polyepoxideresin is selected from the group consisting of diglycidyl ethers ofbisphenols.
 30. The method of claim 23 wherein the polyepoxide resin isincluded in an amount of from about 37 wt. % to about 48 wt. %.
 31. Themethod of claim 23 wherein the polyolefinically unsaturated monomer isselected from the group consisting of acrylic and methacrylic resins,vinyl monomers, unsaturated polyesters solubilized in vinyl monomers andmixtures thereof.
 32. The method of claim 31 wherein thepolyolefinically unsaturated monomer is selected from the groupconsisting of trimethylolopropane trimethacrylate, trimethylolpropanetriacrylate, dipentaerythritol monohydroxypentaacrylate, pentaerythritoltriacrylate, ethoxylated trimethylolpropane triacrylate, 1,6-hexanedioldiacrylate, neopentyl glycol diacrylate, pentaerythritol tetraacrylate,and 1,3-butylene glycol diacrylate.
 33. The method of claim 23 whereinthe polyolefinically unsaturated monomer is included in an amount offrom about 10 wt. % to about 30 wt. %.
 34. The method of claim 23wherein the photoinitiator is selected from the group consisting ofsubstituted benzophenones, substituted acetophenones, benzoin and itsalkylethers, xanthone and substituted xanthones and mixtures thereof.35. The method of claim 34 wherein the photoinitiator is selected fromthe group consisting of 2-hydroxy-2-methyl-1-phenyl-propan-1-one and2-benzyl-2-(dimethylamino)-1- 4-(4-morpholinyl)phenyl!-1-butanone. 36.The method of claim 35 wherein the photoinitiator is included in anamount of from about 1 wt. % to about 10 wt. %.
 37. The method of claim23 wherein the carboxylic acid anhydride is selected from the groupconsisting of methyltetrahydrophthalic anhydride,methylhexahydrophthalic anhydride, chlorendic anhydride, nadic methylanhydride and mixtures thereof.
 38. The method of claim 37 wherein theanhydride is included in an amount of from about 33 wt. % to about 43wt. %.
 39. The method of claim 23 wherein the anhydride accelerator isselected from the group consisting of dicyandiamide, borontrifluoride:amine complexes, boron trichloride:amine complexes, latentamine curatives, tertiary amines, aromatic polyamines, dissociable aminesalts, imidazoles and mixtures thereof.
 40. The method of claim 39wherein the anhydride accelerator is selected from the group consistingof benzyl dimethylamine, 1-(2-cyanoethyl)-2-ethyl-4-methylimidazole,2-ethyl-4-methyl imidazole, and 2,4-diamino-62'-methylimidazolyl-(1)'!ethyl-s-triazine isocyanurate adduct.
 41. Themethod of claim 23 wherein the anhydride accelerator is included in anamount of from about 0.1 wt. % to about 5.0 wt. %.
 42. The method ofclaim 23 wherein said viscosity remains from about 300 centipoise toabout 2,000 centipoise for a minimum of about 6 hours at a temperatureof from about ambient temperature to about 60° C.